A switching device of this kind is presented for example in U.S. Pat. No. 5,680,084 A. The housing described in the respective patent is filled with a gas mixture containing hydrogen. There are known other switches in which one or a multitude of pairs of contacts are provided and which are operated in air. When breaking such a switch, a switching arc is produced between the pair of contacts. In alternating current applications, this switching arc produced between the contacts extinguishes at the natural zero passage of the current, producing a permanent interruption of the current flow. Especially in case of higher currents, the switching arc is driven away from the contacts and extended until it extinguishes due to deionization and cooling, this being achieved by a magnetic blowout field, which is generated by an external system of permanent magnets or a self-magnetic field in the switch itself generated by current paths arranged accordingly. There are switches with known quench systems, for example in the form of what are called deionizing chambers, where the switching arc is separated into a multitude of partial arcs and cooled simultaneously by the chamber walls and baffle plates, causing a fast increase of the voltage of the switching arc and therefore the arc is quenched not later than when the driving voltage is reached, thus causing a permanent interruption of the electrical current.
Depending on the energy content of the arc, this process causes a variable level of thermal load on the contact arrangement, together with a certain burn-off of the contact material. Thermal load is also generated to the switching chamber walls and the arc chutes, resulting in a limitation of the electrical useful life of the switching device. The switching device is exposed to high load during the switching process especially in case of higher arc-power, more especially in case of reduced or missing mobility of the arc, causing a similarly high burn-off of contacts and material changes of the switching chamber walls due to localized high thermal load.
A high thermal load of the switching chambers is generated especially in case of high direct currents, which contrary to similar alternating currents, have no sinusoidal current curve with a natural zero passage of the current, and therefore when disconnecting the contacts, they generate a constant high-power arc. To ensure a maximum possible useful life of a switching device for direct current applications, it is therefore indispensable to minimize the burning time of the switching arc through fast cooling and deionization of the switching path. In this process the burning voltage is increased rapidly, which causes the extinguishing of the arc when the driving voltage is reached.
In case of known arrangements for extinguishing direct currents, where the switching arcs are driven by magnetic blowout fields into what are called deionizing chambers and quenched in these chambers, especially energy-rich arcs can often re-ignite. In this case in a section of the switching path, where the arc no longer has any direct effect, and thus the electrical conductivity is significantly reduced in this area due to the deionization of the surrounding air, the respective section is re-ignited again by the arc, together with a sudden drop of the arc voltage. Repeated re-ignitions can significantly extend the total burning time of the switching arc, which in turn causes an increased thermal load to the switching device. Switching processes with frequent re-ignitions cause therefore a reduction of the useful life of the switching device.
A very efficient extinguishing of the arc is achieved when instead of normal air as the switching environment, hydrogen or a gas mixture containing hydrogen is used in a hermetically sealed housing of the switch. It is known that due to the significantly higher particle velocity of hydrogen molecules as compared to air molecules, hydrogen molecules produce a very efficient cooling and deionization of the switching path. As a result, in case of switching in a hydrogen atmosphere, the arc voltage of a freely burning arc is several times higher than the voltage achievable in air with the same switching arrangement. In practice, this means that by specifically extending the switching arc by a magnetic blowout field, a higher arc voltage can be generated as compared to the voltage reached by separating the arc into a multitude of partial arcs through a classical arrangement using baffle plates.
Encapsulated switching devices filled with hydrogen are found in several products today in the form of compact relays for currents up to several hundred amperes. These products are designed especially as having a very compact arrangement to carry the currents of this magnitude continuously and switch these currents typically several thousand times. With these compact switching chambers, however, the number of switching operations achievable is limited in case of high switching power due to the gradually decreasing insulating strength.